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Improved ground-state modulation characteristics in 1.3 μm InAs/GaAs quantum dot lasers by rapid thermal annealing.

Zhao H, Yoon SF, Ngo CY, Wang R - Nanoscale Res Lett (2011)

Bottom Line: The choice of annealing conditions was determined from our recently reported results.With reference to the as-grown QD lasers, one obtains approximately 18% improvement in the modulation bandwidth from the annealed QD lasers.In addition, the modulation efficiency of the annealed QD lasers improves by approximately 45% as compared to the as-grown ones.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore. zhao0097@e.ntu.edu.sg.

ABSTRACT
We investigated the ground-state (GS) modulation characteristics of 1.3 μm InAs/GaAs quantum dot (QD) lasers that consist of either as-grown or annealed QDs. The choice of annealing conditions was determined from our recently reported results. With reference to the as-grown QD lasers, one obtains approximately 18% improvement in the modulation bandwidth from the annealed QD lasers. In addition, the modulation efficiency of the annealed QD lasers improves by approximately 45% as compared to the as-grown ones. The observed improvements are due to (1) the removal of defects which act as nonradiative recombination centers in the QD structure and (2) the reduction in the Auger-related recombination processes upon annealing.

No MeSH data available.


Related in: MedlinePlus

Plot of ln(Jth) vs. temperature of the as-grown (square) and 600°C annealed (circle) QD lasers.
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Figure 6: Plot of ln(Jth) vs. temperature of the as-grown (square) and 600°C annealed (circle) QD lasers.

Mentions: Figure 6 shows the logarithmic values of threshold current densities (ln(Jth)) of as-grown and 600°C annealed devices measured as function of temperature. The as-grown and 600°C annealed lasers exhibit infinite T0 at temperature range of 10-65 and 10-70°C, respectively. The infinite T0 could be explained by the increase in Auger recombination and improved carrier thermalization with increasing temperature. The former will increase the threshold current, while the latter decreases the threshold current by increasing the efficiency of the radiative recombination due to thermal escape of carriers from the dots and transfer into deeper levels (larger dots) [1]. Due to p-type modulation doping in the QDs, the electrostatic attraction of the excess holes increases the effective barrier for electron escape, thus limits the electron thermalization till higher temperature as compared to the intrinsic device and results in a larger T0 [18]. The as-grown laser exhibits T01 ~ 77.9 K from 70 to 100°C. ES-dominated lasing starts at 105°C in the as-grown laser. However, in the annealed laser, GS lasing dominates throughout the measured temperature range, up to 120°C. The annealed laser exhibits T01 ~ 249 K from 75 to 120°C. As shown in Figure 6, as compared to the as-grown lasers, the threshold current has been reduced and T01 has been improved for the annealed QDs up to 120°C. These are possibly due to the reduction in Auger recombination in the annealed QDs since Auger recombination increases the threshold current. In agreement with the work of Shchekin et al. [19], the modulation response of QD laser is closely related to the threshold characteristics. Although QDs have been predicted to be modulated at very high frequencies theoretically, it has been shown by Deppe et al. [4] that the current densities required to reach these values should be considered. The low threshold current density of the annealed QD laser suggests that this device can be driven far above threshold and reaches higher speed. It has been pointed out by Marko et al. that Auger recombination is an important loss process in 1.3 μm QD lasers around room temperature [18]. p-Doping of the QDs enhances the gain, but it also increases the threshold current, possibly due to increased Auger recombination [20]. The improved T0, together with the reduced threshold current density in the annealed lasers, implies that the severe nonradiative Auger recombination is possibly reduced as a consequence of thermal annealing by reducing the defect densities. And this potential results in improved carrier relaxation, thus improved high-speed modulation characteristics.


Improved ground-state modulation characteristics in 1.3 μm InAs/GaAs quantum dot lasers by rapid thermal annealing.

Zhao H, Yoon SF, Ngo CY, Wang R - Nanoscale Res Lett (2011)

Plot of ln(Jth) vs. temperature of the as-grown (square) and 600°C annealed (circle) QD lasers.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211475&req=5

Figure 6: Plot of ln(Jth) vs. temperature of the as-grown (square) and 600°C annealed (circle) QD lasers.
Mentions: Figure 6 shows the logarithmic values of threshold current densities (ln(Jth)) of as-grown and 600°C annealed devices measured as function of temperature. The as-grown and 600°C annealed lasers exhibit infinite T0 at temperature range of 10-65 and 10-70°C, respectively. The infinite T0 could be explained by the increase in Auger recombination and improved carrier thermalization with increasing temperature. The former will increase the threshold current, while the latter decreases the threshold current by increasing the efficiency of the radiative recombination due to thermal escape of carriers from the dots and transfer into deeper levels (larger dots) [1]. Due to p-type modulation doping in the QDs, the electrostatic attraction of the excess holes increases the effective barrier for electron escape, thus limits the electron thermalization till higher temperature as compared to the intrinsic device and results in a larger T0 [18]. The as-grown laser exhibits T01 ~ 77.9 K from 70 to 100°C. ES-dominated lasing starts at 105°C in the as-grown laser. However, in the annealed laser, GS lasing dominates throughout the measured temperature range, up to 120°C. The annealed laser exhibits T01 ~ 249 K from 75 to 120°C. As shown in Figure 6, as compared to the as-grown lasers, the threshold current has been reduced and T01 has been improved for the annealed QDs up to 120°C. These are possibly due to the reduction in Auger recombination in the annealed QDs since Auger recombination increases the threshold current. In agreement with the work of Shchekin et al. [19], the modulation response of QD laser is closely related to the threshold characteristics. Although QDs have been predicted to be modulated at very high frequencies theoretically, it has been shown by Deppe et al. [4] that the current densities required to reach these values should be considered. The low threshold current density of the annealed QD laser suggests that this device can be driven far above threshold and reaches higher speed. It has been pointed out by Marko et al. that Auger recombination is an important loss process in 1.3 μm QD lasers around room temperature [18]. p-Doping of the QDs enhances the gain, but it also increases the threshold current, possibly due to increased Auger recombination [20]. The improved T0, together with the reduced threshold current density in the annealed lasers, implies that the severe nonradiative Auger recombination is possibly reduced as a consequence of thermal annealing by reducing the defect densities. And this potential results in improved carrier relaxation, thus improved high-speed modulation characteristics.

Bottom Line: The choice of annealing conditions was determined from our recently reported results.With reference to the as-grown QD lasers, one obtains approximately 18% improvement in the modulation bandwidth from the annealed QD lasers.In addition, the modulation efficiency of the annealed QD lasers improves by approximately 45% as compared to the as-grown ones.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore. zhao0097@e.ntu.edu.sg.

ABSTRACT
We investigated the ground-state (GS) modulation characteristics of 1.3 μm InAs/GaAs quantum dot (QD) lasers that consist of either as-grown or annealed QDs. The choice of annealing conditions was determined from our recently reported results. With reference to the as-grown QD lasers, one obtains approximately 18% improvement in the modulation bandwidth from the annealed QD lasers. In addition, the modulation efficiency of the annealed QD lasers improves by approximately 45% as compared to the as-grown ones. The observed improvements are due to (1) the removal of defects which act as nonradiative recombination centers in the QD structure and (2) the reduction in the Auger-related recombination processes upon annealing.

No MeSH data available.


Related in: MedlinePlus